Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share	4,013	3,090
Common Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share	3,990	3,040
Unvested Common Stock Subject to Repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share	23	50